Reflex superregenerative receiver



March 18, 1952 1 c, TE| |ER REFLEX SUPERREGENERATIVE vRECEIVER Filed sept. 5, 194e SSQR Q&@@\

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INVENTOR. fJP/f 6'. Tal/E Patented Mar. 18, 1952 2,589,455 REFLEX SUPERREGENERATIVE RECEIVER Joseph C. Tellier, Penn Wynne, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application September 5, 1946, Serial No. 695,017

(Cl. Z50-20) 6 Claims. l

This invention relates to vacuum tube oscillators and their applications. More specifically, it relates to a special form of vacuum tube oscillator adapted to oscillate alternately at two different frequencies, and which is particularly adapted for use as a detector of angular velocity-modulated carrier wave signals.

In the latter connection there is described, in Patent 2,351,193 of June 13, 1944, to Murray G. Crosby for a Frequency Modulation Detector Circuit, a method of detecting angular-velocity modulated carrier wave signals whereby two superregenerative detectors are operated at different frequencies respectively above and below the center, or carrier, frequency of the angular-velocity modulated carrier wave signal to be detected. The two detectors are alternately quenched and unquenched to permit oscillations to build up in their tank circuits at a rate determined by the extent of modulation of the carrier wave signal at the time of unquenching. The outputs of the two detectors are combined so as to yield a signal which varies in accordance with the angular velocity modulation of the input carrier, but which is substantially independent of variations in the amplitude of said carrier. The circuit shown in the patent for applying this method employs separate tubes for the two superregenerative oscillators, two additional tubes comprising a quench controlling oscillator, and yet another tube to vary the tuning of a common tank circuit used in conjunction with both superregenerative oscillators.

It is an object of the present invention to provide a novel and improved circuit, adapted to operate substantially in accordance with the method of the aforementioned patent, in which the number of tubes employed is reduced to two, or their equivalent. This objective is achieved by reflexing the tubes to operate both separately as superregenerative oscillators and, in cooperation one with the other, as a quench controlling oscillator. In this manner the need for a separate is desired alternately to generate oscillations at two substantially different frequencies, and it therefore has other applications which need not here be enumerated.

The principles of the invention and its mode of operation will be fully understood upon consideration of the following description, making reference to the drawings in which:

Figure 1 is the schematic diagram of a representative embodiment of the invention, and

Figures 2, 3, 4 and 5 are diagrams which will be referred to in explaining the principle of the invention and the operation of the embodiment in accordance with Figure 1.

Referring to Figure 1, the low frequency oscillator, which controls the quenching and unquenching of the two separate superregenerative detectors above referred to, comprises the triode vacuum tubes I and 2 and tuned circuits 3 and 4 plus other components hereinafter to be mentioned. Tuned circuits 3 and 4 comprise condensers 5 and 'I respectively and inductors 6 and 8 respectively. Each of these circuits is connected between the plate of one of the oscillator tubes and a source of positive potential. Both circuits are tuned to resonate at the desired quench frequency, which preferably should be outside the audible range, yet as low as possible to provide for a relatively long build-up time between successive unquenchings of each superregenerative oscillator. The latter condition is conducive to high sensitivity in the superregenerative oscillators, the need for which will hereinafter become apparent.

Also included in the low frequency, or quench, oscillator circuit are resistors 9 and II and condensers Ill and I2. The resistors 9 and II respectively are included in the connections from the grids of tubes I and 2 to ground, while condensers I0 and I2 respectively connect the grids of each of these tubes to the plate of the other. The time constants of the RC circuits, formed respectively by resistor 9 and condenser I ll and by resistor Il and condenser I2, are determined in accordance with the frequency of the low frequency oscillator, and, if, for example, this is 50 kilocycles, the compcnent values may be as follows:

Resistors 9 and II ohms 100,000 Condensers I0 and I2 mi farads 1,000

The oscillator thus constituted is very similar, both as to configuration and mode of operation, to a conventional multivibrator. It is here used, in place of the somewhat less complicated multivibrator, to generate a substantially sinusoidal quenching wave, whereby suicient time is permitted to elapse, between the quenching of one superregenerator and the unquenching of the other, to prevent ringing of the tank circuit which is common to both of the superregenerative oscillator circuits hereinafter to be described. In other applications of the invention than the one presently to be described, however, it may be found desirable to utilize another form of low frequency oscillator, such, for example, as the multivibrator, and it is to be understood that the invention contemplates the use of such other forms.

Y Triodes I and 2 also cooperate individually with tuned circuit I3, comprising condenser I4 and inductor I5, to form two distinct and separate superregenerative oscillators. To this end, the grids of the two triodes are connected respectively through condensers I6 and I8 to one side of parallel-tuned circuit I3. The other side of the tuned circuit may be connected to ground as shown. The cathodes of both triodes I and 2 are connected to a common tap on inductor I 5 of tuned circuit I3, so that a portion of inductor I5 is included in both grid and plateV circuits of both triodes. This provides, in Veach instance, the necessary feedback required for oscillation. In order that one of the superregenerative oscillators may have a frequency of oscillation different from that of 'the other, condenser is included 'in' the connection from the cathode of triode 2 Ato the tap on inductor I5. Tuned circuit I3 maygfor example, have aV resonant frequency somewhere in the range of from to 50 megacycles, andicondenser 2B may have a value of 40ML farads, which will be such as to produce a differenceL in the frequencies of osci'llationof'th'e two superregenerators of rapproximately 200 kilocycles. The .presence of condenser 20"makes necessary the provision of a D.'C. return to'ground for the cathodes of tubes Iv and 2.Y This is provided, without shortcircuiting tank .circuit I3, by means of a choke 38 which is preferably self-resonant at the same frequency as ytuned circuit I3. Included inthe connections from' the grids of each of tubes I and 2 to ground, `are` resistors I'I and I9 respectively. The RC circuits thus-formed by condenser I6 and resistor .II, and vby condenser 'I8 and resistor f I9, mayhave'tine constants` corresponding to the frequenciesof oscillation ofthe two superregenerativeoscillators. Thus, for example, condensers Iii and `Iii'may each have a value of SOM-farads, while resistors I'I and I9 may have Values of 10,000 ohms. The latter values will be suiiiciently small, compared `to the values of resistors!) and `II,- to permit operation of the low frequency or quench oscillator in the manner hereinbefore described.` Atthe same time, they will serve as Yisblating resistors to prevent undue loading of tuned circuit YI3 lowing/to the presence of 'condensers' I0' and I2 in-the low frequency oscillating circuit;Y Condensers 2I` and 22 serve to by-p'ass componentsat the super-regenerative oscillator frequencyfrom the 4plates of tubes I and-2 respectively to ground, and each may have a value of 100W-fands. 'Resistors I'I`and I9 perform additional functions, -as will` presently be set forth, in shaping the quench waveforms applied to the grids of tubes` I and 2, and in developing the necessary`self-biases for operation yo f the two superregenerative oscillators.

The quench,wave`form'-produced by the low frequency 'oscillator is applied to the grids of tubes I and 2 in phase opposition, so that, while the potential at point 25 is positive with respect to ground, that at point 26 is negative, and vice versa. In the absence of resistors I'I and I9, the quench Waveform applied to the grid of one of the tubes would be substantially as represented in Figure 2. This would cause the grid potential of the tube to rise substantially above cut-off level so that the build-up of oscillations in tank circuit I3 would depend upon the mutual conductance of the tube. It is unlikely that the characteristics of the two tubes would be identical, and this would give rise to discrepancies between the modes of operation of the two superregenerators which would adversely aiect the ability of the system as a whole to eliminate amplitude modulation in the received signal. The presence of resistors I'I and I9 avoids this difdeulty by limiting the amplitudes of the quenching'signals applied to the grids of tubes I and 2 in the manner shown in Figure 3. This is accomplished by reason ofthe fact that the grid of each tube draws current as it goes positive, and thereby negative biases are developed across resistors I'I and I9 respectively to compensate the rise in potential above ground at'points 25 and 26.

At a time subsequent tothat'at which the pctentialonthegrid of either of tubes I or 2v reaches and slightly exceeds the cut-olf level, oscillations of appreciable amplitude lwill commence Vto build up in tuned circuit I3. Such commencement of oscillations will occur sooner ,or later, after this point of unquenching has been reached, depending uponV the amplitude and frequency of signal present -i-n tank rcircuit I3 at the time of unquenching. As these oscillations build up, selfbias is `developed across either resistorV I'I or resistor I9, so that successive RF peaks in the voltage developed across tuned circuit I3 tend to exceed this self-bias by only a relativelyv small amount; Thus oscillations-are permitted to build up to ya substantial value before tube overload occurs. LAfter overload has occurred, oscillation will continue at approximately the overload level until the potential of the quench-controlling signal falls sufficiently to cause the tube to cut off.

As a v`result of delayV in the commencement of build-up of oscillations, after the time at which unquenching occurs, the waveformvappearing on the grid of the oscillator tube will be modified so as to correspond, for example, to the solid line representation in Figure 4. For different values of signal in tank circuit I3 at the time of unquenching, buildup may commence at different times, and the quenching waveform appearing on the grid of the tube will be correspondingly modified as represented by the broken line modifications in Figure 4. More specifically, if a modulated carrier wave signal is impressed uponA tank circuit I3; the time at which oscillations commenceto build up-will depend upon the instantaneous value of modulation at the time when one of the oscillator tubes commences to conduct. Thus theV durations of Vsuccessive'unquenched intervals of each superregenerator circuit, and hence the magnitudes of their outputs.; will vary as a function of the modulation ofthe input carrier wave signal." Concurrently the `wave appearing on the gridV of each tube will vary at the modulation rate so-as, for example, to'assumeyduring each cycle,'one of the representative forms shown'inFigure 4.

When the circuit is used as a detector of angular-velocity modulated carrier wave signals, input signal from an antenna 23 may be supplied to tank circuit VI3 through an inductor 24 coupled to tank circuit inductor I. Output from each ofthe superregenerative oscillators may be derived across resistors 21 and 28, respectively connected in series with inductors 6 and 8 of tank circuits 3 and 4 of the low frequency, or quench, oscillatorf Resistors 21 and 28, whose values may be 1,000 ohms each, are preferably by-pas'sed by series resonant circuits 29, and 3|, 32 respectively, each tuned to the quench frequency. The values of condensers 29 and 3| and of resistors 2`|V and 28 may be made such as to deemphasize high frequency components of the detected signal. This is desirable when, as is customary in FM transmission, high frequency components of the intelligence signal are emphasized, before being used to modulate a high frequency carrier, in order to reduce the effect of noise upon them in the course of transmission and reception. Thus, for example, condensers 29 and 3| may each have a value of 0.1 ,lL-farad while inductors 3| and 32 may have values of 100 ,ii-henries. The separate detected outputs from the'two superregenerative oscillators, developed across resistors 2l and 28 respectively, are supplied through coupling condensers 33 and 34 to the grids of tubes 35 and 36. These tubes serve to subtract the outputs from the two separate detectors so as to yield, across terminals 3l, a detected `output signal containing variations corresponding to the frequency or phase modulation of the input signal, but in which variations in the amplitude of-said signal are substantially eliminated. The reason for this will be apparent from a consideration of Figure 5.

A'-Ihe oscillating frequencies of the two superregenerative detectors of the circuit of Figure l are adjusted so as vto be displaced by equal amounts on either side of the center or carrier frequency of the angular velocity-modulated carrier wave signal to be received. This yields the two overlapping frequency response characteris-y tics 39 and 40 as shown in Figure 5 with center frequencies f1 and f2, respectively above and below the center carrier frequency fo. In the absence of frequency modulation of the input signal, the outputs of both superregenerative receivers will be equal Vand will correspond to the ordinate foe, as shown in Figure 5. Subtraction of these two signals in the amplifier comprising tubes 35 and 36 in the circuit of Figure 1 will produce a net output of zero. 1f the frequency of the input carrier wave signal is modulated so as to deviate below the center frequency fo to a frequency f3, then the outputs of the two oscillators will be represented respectively by the ordinates fsa. and fab in Figure 5. The difference between these two, and hence the net output of the detector derived at terminals 31 in Figure l, will be proportional to the difference, ab, between these two ordinates. Likewise, if the input carrier wave signal is modulated so as to deviate to a frequency f4 above the center frequenci7 fo, the outputs of the two detectors will correspond to the ordinates flic and f4d respectively. In this instance the net output at terminals 3l will be proportional to the difference, cd, between these two ordinates. Variations in the amplitude of the input carrier wave signal will produce ,corresponding increases in the outputs from both detectors, regardless of the amount by which the frequency of the signal is deviated, and such increases in output will tend to cancel out in the output from tubes 35 `and 36 derived at output terminals 3l.

Although the invention has been particularly described with reference to its application as a detector of angular-velocity modulated carrier wave signals, it will be apparent to those skilled in the art that, basically, the arrangement shown in Figure 1 is an oscillator for alternately producing oscillations at two different frequencies. As such it has numerous other applications. Also it will be apparent that certain modifications to the circuit shown in Figure 1 may be made with# out departing from the scope of the invention as defined in the appended claims. Thus, with ref erence to the embodiment disclosed, it is not essential that the two tubes, which function separately and individually as superregenerative oscillators, both be employed, in cooperation one with the other as shown, to constitute a balanced push-pull low frequency quench oscillator. Although, both ytubes being available, it appears preferable touse them in this manner, it 'is equally feasible, as will readily be apparent, to use but one of them to form a low frequency oscillator to control the quenching of both superregenerative oscillators. Such a circuit is achievable by combining tank circuits 3 and 4 in the embodiment of Figure l and by making other slight and obvious modifications to the circuit. Other modifications of a like nature will readily occur to' those seeking to apply the invention in accordance with the principles hereinbefore set forth. I claim: Y e

l. 1n a superregenerative receiver of angularvelocity modulated carrier wave signals, a tank circuit resonant at a relatively high frequency and supplied with said modulated signals, arst oscillator comprising said tank circuit together with a vacuum tube and first means coupling said tank circuit to said vacuum tube, a second oscillatorcomprising said tank circuit and another vacuum tube together with secondl means coupling said tank circuit to said other vacuum tube, each of said tubes having at least trioder elements, means included in said coupling means for causing said first and second oscillators to oscillate at rdifferent frequencies respectively above and below said carrier frequency, a third oscillator comprising said tubes and a pair of tuned circuits, each tuned to a frequency lower than said first resonant frequency and each connected in the plate circuit of one of said tubes, said tuned circuits cooperatingwith said tubes to produce oscillations at a relatively low frequency as determined by said tuned circuits so as to render said tubes alternately conducting, wherebysaid separate oscillators are rendered alternately and intermittently operative as superregenerative ampliers, means included in the plate circuits of each of said tubes for deriving outputs from said separate oscillators, and means combining said outputs to yield a signal which varies in substantial accordance with the frequency deviation of said modulated carrier.

2. Ina vacuum tube oscillator system. a tank circuit resonant at a relatively high frequency, a first oscillator comprising said tank circuit and a vacuum tube associated therewith together with means coupling said tank circuit to said tube, a. second oscillator comprising said tank circuit and another vacuum tube together with second means coupling said tank circuit to said tube, each of said tubes having at least triode elements, means included in said coupling means for causing said first and second oscillators to oscillate at different frequencies, and a third oscillator comprising said tubesr and a pair of tuned circuits. each tuned to a frequency lower than said first resonant frequency and each connected in the plate circuit of one of said tubes, said tuned circuits cooperating with said tubes to produce oscillations :at arelative1y-l0w:frequency as determlned vbysaid tuned circuits. so vas to render lSaid tubes alternately conducting, whereby said iirst and Vseeond oscillators are rendered alternately and intermittently operative. Y

3; In a vacuum tube oscillator system: a rst oscillator operating at a relatively low frequency and comprising aV pair of vacuum tubes together with circuit means for rendering said tubes alternately conductive; a first intermittently-operative Voscillator comprising a tuned circuit resonant at a relatively high frequency, one of said alternately-conductive vacuum tubes, and means coupling said tuned circuit to said last-named tube; a vsecond. intermittently-operative oscillator comprising said tuned circuit and the other of said vacuum tubes. together with second means coupling `said tuned circuit to said other tube; each ofsaid intermittently-operative oscillators being operative only during intervals of conduction of the vacuumftube which it comprises; the effective Aimpedance of said rstcoupling means differing from that of said second coupling means byv an amount sufcientto produce substantially different oscillation frequencies in said rst and second oscillators during their respective periods` of operation.

sfysterninV accordance with Vclaim v3, in which s aid firstoscillator includes reactive means forfpreventng yboth of said vacuum tubes from conducting-iw asubstantial period of time betweenfsuccessive intervals of conduction thereof.

.5. vIn avacuum rtube oscillator system: a rst Y oscillator comprising a -pair of vacuum tubes and a tuned circuit resonantI at a relatively low frequency andcoupled to said vacuum tubes; means included in said oscillator for establishing phase oppositionof theoscillations thereof at the grids ofsaid tubes whereby said tubes are rendered coupling means by an amount sulcient to produce substantially diierent oscillation frequencies in said second and third oscillators.

6. In a superregenerative receiver of angular velocity modulated carrier wave signals, a ilrst oscillator comprising a pair of vacuum tubes and adapted to oscillate at a relatively low frequency; a tuned circuit resonant at a relatively high frequency and supplied with said modulated signals; a second oscillator comprising said tuned circuit together with one of said vacuum tubes and first means coupling said tuned circuit to said lastnamed vacuum tube; a third oscillator comprising said tuned circuit and the other of said vacuum tubes together with second means coupling said tuned circuit to said other tube; the effective impedance of said first coupling means dilering from that of said second coupling means by an amount sufcient to cause said second and third oscillators to oscillate at substantially different frequencies, the frequencies of said second and third oscillators lying respectively above and below the frequency of said carrier waves; means causing said first oscillator to render said vacuum tubes alternately conducting, whereby said second and third oscillators are rendered alternately and intermittentlyY operative as superregenerative amplifiers; and means deriving outputs from said second and third oscillators and combining said outputs to yield a signal which varies in substantial accordance with Vthe frequency deviation of said modulated carrierwave.

JOSEPH C. TELLIER.

REFERENCES CTED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,424,065 Armstrong July 25, 1922 1,787,979 Hansell J an. 6, 1931 2,091,546 Hruska Aug. 31, 1937 2,297,926 Usselman Oct. 6, 1942 2,351,193 Crosby June 13, 1944 2,363,651 Crosby Nov. 28, 1944 2,416,794 Crosby Mar. 4, 1947 FOREIGN PATENTS Number Country Date 389,225 Great Britain Mar. 16, 1933 

